Action of endogenous atrial natriuretic peptide in calves with experimental acute central venous congestion and low cardiac output.

STUDY OBJECTIVE: The aim of the study was to investigate plasma concentrations of atrial natriuretic peptide, aldosterone, and renin during experimentally induced acute central venous congestion. DESIGN: Two experimental calf models were used: (1) right heart failure due to pulmonary artery obstruction; (2) inferior vena cava syndrome produced by inferior vena caval obstruction. Hormonal responses and haemodynamic variables were measured over 6 h. SUBJECTS: Experiments were performed on three female "Schwarzbund" calves, age 3 months, weight 92 +/- 8 kg. MEASUREMENTS AND MAIN RESULTS: In the pulmonary artery obstructed group there was an increase of plasma aldosterone from 6.5(SEM 1.6) to 22.1(3.2) ng.dl-1 (p less than 0.05), of renin from 0.7(0.1) to 2.5(0.3) Goldblatt units x 10(-4).ml-1 (p less than 0.05), and of atrial natriuretic peptide from 22.1(4.5) to 141.4(27.8) pmol.litre-1 (p less than 0.05). During inferior vena caval obstruction, aldosterone increased from 2.4(0.4) to 20.9(2.0) ng.dl-1 (p less than 0.05), and renin increased from 0.4(0.05) to 2.0(0.20) Goldblatt units x 10(-4).ml-1 (p less than 0.05). In this experiment, atrial natriuretic peptide remained unchanged. Cardiac output decreased in both groups. There was significant fluid and electrolyte retention during both experiments, with urine volume decreasing from 87.7(11.6) to 35.0(1.2) ml-h-1 in experiment (1), and from 185(14) to 95.7(8.6) ml.h-1 in experiment (2). CONCLUSIONS: The study suggests (1) that in an experimental acute state of reduced cardiac output due to pulmonary artery stenosis with constantly increased right heart pressures, raised endogenous atrial natriuretic peptide failed to induce diuresis and natriuresis; (2) that in acute right heart failure, renin and aldosterone secretion could not be suppressed by raised atrial natriuretic peptide concentrations; and (3) atrial natriuretic peptide secretion seemed to be exhausted after 6 h continuous atrial distension.

Streptococcus pneumoniae mycotic aortic aneurysm after allogeneic bone marrow transplantation.

BACKGROUND: Streptococcus pneumoniae (SP) is a common cause of community-acquired pneumonia and accounts for up to 30% of all cases of pneumonia. Patients with chronic graft-versus-host-disease (GvHD) after allogeneic bone marrow transplantation (BMT) have a high susceptibility to SP infections. So far, mycotic aneurysm resulting from SP has not been reported after BMT. METHODS: We report on a patient with extensive, chronic GvHD who developed low back pain 22 months after allogeneic BMT. RESULTS: Computed tomography of the abdomen displayed mycotic, saccular aneurysmatic enlargement of the infrarenal aorta, with leakage of contrast medium into the aneurysm. The aneurysm was resected, and the defect was closed with an autologous patch from the internal iliac artery. Bacteriologic samples from the abscess grew SP. The patient recovered uneventfully. CONCLUSIONS: This observation confirms the importance of pneumococcal prophylaxis after BMT and suggests that an aggressive diagnostic approach should always be considered in patients with chronic GvHD, even if they present with nonspecific symptoms.

Numerical study of wall mechanics and fluid dynamics in end-to-side anastomoses and correlation to intimal hyperplasia.

In order to analyse the wall mechanics and the flow dynamics in compliant vascular distal end-to-side anastomoses, computer simulation has been performed. In a model study the effect of compliance mismatch on the wall displacements and on the intramural stresses as well as the influence of wall distensibility on the flow patterns are demonstrated applying two distensible models with different graft elasticity. In addition, the flow in a rigid model simulating a vein graft without adaption of the venous lumen has been investigated. The geometries for these models were obtained from a concurrent experimental study, where the formation of distal anastomotic intimal hyperplasia (DAIH) was studied in untreated and externally stiffened autologous venous grafts in sheep. In the flow study the time-dependent, three-dimensional Navier-Stokes equations describing the motion of an incompressible Newtonian fluid are applied. The vessel wall is modelled using a geometrically non-linear shell structure. In an iteratively coupled approach the transient shell equations and the governing fluid equations are solved numerically using the finite element method. In both compliant models maximum displacement and areas of steep stress gradients are observed in the junction region along the graft-artery intersection. The comparison of the normal deformations and the distribution and magnitude of intramural stress shows quantitative differences. The graft elasticity acts as a regulating factor for the deformability and the stress concentration in the junction area: In the model with high graft-elasticity maximum normal deformation at the side wall is 17%. This is twice as large as in the stiff graft model and maximum principle stress at the inner surface differs by one order of magnitude. The numerical results concerning the flow patterns indicate strongly skewed axial velocity profiles downstream of the junction, large secondary motion, flow separation and recirculation on the artery floor opposite the junction and at the inner wall downstream of the toe. In these regions a correlation between the time-averaged fluid wall shear stress and intimal thickening found in the animal experiment can be observed, whereas the pronounced formation of DAIH at the suture line seems to be mainly dependent on wall mechanical factors such as intramural stress and strain.

Collagen patch coated with fibrin glue components. Treatment of suture hole bleedings in vascular reconstruction.

BACKGROUND: Bleeding from suture holes during vascular reconstruction, particularly when polytetrafluoroethylene (PTFE) prostheses are used, is still a problem which can lead to intraoperative delay and increased blood loss. The aim of this prospective, randomised, open, controlled multicentre study was to evaluate whether the use of a new local haemostyptic would reduce intraoperative blood loss and the time to haemostasis. METHODS: Thirty patients received a new haemostyptic (TachoComb H, Nycomed Pharma AG), whereas another 30 patients were treated with compresses. The vascular reconstructions were either anastomoses or patch angioplasties and were performed using PTFE vascular prostheses. RESULTS: The mean time to haemostasis of suture hole bleeding in the haemostyptic group (326.0 sec) was significantly shorter compared to the control group (514.3 sec) (p=0.006). The median intraoperative blood loss was 24.5 g in the treatment group and 57.3 g in the control group (p=0.045). CONCLUSIONS: It was shown that collagen patches coated with components of fibrin glue significantly reduce the time to haemostasis as well as blood loss at the operation site in patients undergoing vascular reconstruction with PTFE grafts.

Numerical model and experimental investigation of blood flow through a bifurcation. Interaction between an artery and a small prosthesis.

The use of prosthetic vascular grafts as bypass to arteries of small diameter (< 5 mm) often is thwarted by occlusion after months of apparently normal function. This work presents a numeric simulation of the flow through a distal anastomosis. A finite element method has been applied, providing information on the velocity field, streamlines, wall shear stresses, and vorticity in the different geometries. The study illustrates the dependence of the flow pattern and wall shear stress distribution upon Reynolds number, and the results show high shear stresses, approximately 3-5 times larger than normal, acting on the vessel wall at the branching point for the small diameter branch.

Compliance and formation of distal anastomotic intimal hyperplasia in Dacron mesh tube constricted veins used as arterial bypass grafts.

Dilated and varicose veins constricted with a Dacron mesh tube were successfully used as arterial bypass grafts to avoid nonautogenous vascular prostheses. Mesh constriction has also been used to adapt the venous graft lumen to the diameters of grafted arteries. The influence of the external mesh on the wall elasticity of such venous grafts and the reactions of the host artery were not investigated. Elastic properties of mesh constricted autologous veins used as arterial grafts in femoropopliteal reconstructions, as well as consecutive formation of distal anastomotic intimal hyperplasia (DAIH), were investigated in this experiment. Twenty-four autologous venous grafts were implanted in 12 sheep. Grafts were left natural (Groups 1 and 3) or were constricted with an external Dacron mesh (Groups 2 and 4); their diameters were left unchanged (Groups 1 and 2) or were matched to the diameter of the host artery (Groups 3 and 4). Wall elasticity of the graft, distal anastomosis, and distal artery were measured by locally applied crystal transducers during surgery and follow-up. Formation and localization of DAIH was evaluated histomorphologically after a median of 8.3 months. Graft wall elasticity was found to be lower (54.6 vs. 147.9, P = 0.006) and overall DAIH was found to be higher in mesh tube grafts (49.42 vs. 20.8 microns, P = 0.001, Mann-Whitney U-test). No differences in elasticity and DAIH formation were observed between grafts with adapted and large diameters. Constriction of venous grafts by a Dacron mesh tube reduces graft wall elasticity and promotes formation of DAIH. To avoid such an increased mismatch in compliance while making use of the advantages of this method, the external mesh tube must not be brought close to the distal anastomotic area itself.

Effect of stationary guiding vanes on improvement of the washout behind the rotor in centrifugal blood pumps.

In centrifugal pumps, there always exists an area of stagnation between the rear of the rotor and the rear housing wall that promotes thrombus formation around the axle. Some current devices overcome the problem by using holes in the rotor plane, leading to increased hydrodynamic losses and shear stress. In this study, a simple apparatus was developed to overcome this problem. Guiding vanes were fixed to the rear housing wall. These vanes decrease the tangential velocity of the fluid and thus the centrifugal force, leading to an increased secondary flow toward the axle. The effect of such vanes was studied in videographic and ultrasound studies. An increase of washout and mixing between the flow layers could be demonstrated (stay time < 200 msec versus several seconds without vanes). In the first animal experiment using nonoptimized vanes, there was no thrombus at the back plane or the seal, and only a small thrombus at the transition between axle and rotor. Hemolysis was slightly elevated (3.2 mg/dl versus 2.5 mg/dl in control experiments). In conclusion, it is highly likely that this simple system will improve the flow characteristics in centrifugal pumps.

Timing for implantation and transplantation in mechanical bridge to transplantation.

The implantation of a mechanical blood pump in a deteriorating candidate for heart transplantation is indicated in general if the cardiac index is less than 1.9 L/min/m2 despite maximal inotropic support. Deterioration of end organ function may be taken as a second factor indicating the need for mechanical support as patients with acute onset of shock may react differently from patients with chronic deterioration. Preoperative need for dialysis largely reduces the chances of long-term survival. The time on support should be long enough to normalize or at least improve secondarily damaged organ systems, but with time infectious and thromboembolic complications will increase. So optimal periods for artificial heart support range between two days and four weeks. Age less than 40 years is a positive predictor for outcome in TAH bridging. The general guidelines, however, do not preclude a favourable outcome in complicated cases, as we show in our own series.

Minimization of hemolysis in centrifugal blood pumps: influence of different geometries.

Centrifugal blood pumps are of substantial importance for intraoperative extracorporeal circulation and for temporary cardiac assist. Their development and improvement raises many specific questions, especially on mechanical blood properties, flow distribution, and the resulting biocompatibility. In this comprehensive study the influence of various pump geometries on blood trauma was investigated. For this purpose analytical calculations, hydrodynamic performance, numerical simulation, in vitro hemolysis tests and in vivo experiments were used. The gap between rotor and housing was found to be crucial showing a distinct minimum of hemolysis at a gap of 1.5 mm (in vitro increase of plasma free hemoglobin per 100 ml plasma an hour: delta fHb/hour = 2.4 +/- 0.83 mg%/h at 1.5 mm versus 12 +/- 2.2 mg%/h at 2.5 mm; p < 0.05). Housing diameter and shape of the vanes were of less importance for blood traumatization (d = 60 mm: delta fHb/hour = 6.36 +/- 1.8 mg%/h; d = 70 mm: fHb = 7.1 +/- 1.9 mg%/h; straight radial vanes: 5.2 +/- 1.8 mg%/h; straight inclined vanes: 6.8 +/- 1.2 mg%/h; flexed vanes: 6.1 +/- 2.0 mg%/h). Three animal experiments confirmed the optimization of geometry, with a mean fHb of 2.5 to 3.2 mg% in steady state. Hydrodynamic efficiency revealed to be a necessary, but not a sufficient and sensitive criterion for hemolysis minimization (e.g. changes of eta < 10% for changes of fHb > 500%). Numerical simulation gives an improved insight in flow distribution, but can not yet be applied for quantification of blood trauma.(ABSTRACT TRUNCATED AT 250 WORDS)

[Aneurysma spurium after iatrogenic arterial puncture--incidence, risk factors and surgical therapy]. / Das Aneurysma spurium nach iatrogener arterieller Punktion--Inzidenz, Risikofaktoren und chirurgische Therapie.

Due to the markedly increased number of arterial punctures performed during diagnostic angiography and angioplasty procedures for cardiac and peripheral vessel disease, the complication of false aneurysms after arterial puncture has gained increasing significance. The incidence of false aneurysms after puncture reported in the literature ranges from 0.05-2%. However, careful sonographic follow-up may reveal an incidence twice as high. The goal of this retrospective investigation of 28 patients with false aneurysms was to elucidate risk factors leading to failure of spontaneous closure of the arterial site, as well as to examine the symptoms and clinical course of such patients. Pseudoaneurysms became manifest, depending on the method of puncture, on average 16.4 days after the procedure. The highest risk was seen in adipose patients (18 pts., 64.3%). In these patients the number of tangential and multiple vessel punctures was also highest. Further risk factors were local vessel sclerosis, hypertension, diabetes mellitus, poor general condition, and disturbances of blood coagulation. The typical clinical findings were seen in only 13 patients. In 3 patients blood loss was the predominant symptom. Twelve further pseudoaneurysms (42.8%) were found incidentally at follow-up. The diagnosis was made in all patients sonographically. In 1 patient it was initially identified as an incidental finding at angiography. In 25 cases simple vessel reconstruction was possible (stitch or patch). In 3 cases (10.7%) a more extensive procedure involving vessel replacement was necessary. Severe postoperative complications included local infection (in 2 patients, 1 of whom also had a recurrent false aneurysm) and arterial bleeding necessitating surgical intervention (1 patient).(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of Chlamydia pneumoniae DNA in atheromatous tissues by polymerase chain reaction.

Chlamydia pneumoniae is an important human respiratory pathogen. Recently, seroepidemiological data and the demonstration of chlamydial DNA or antigen within parts of atherosclerotic lesions have suggested a causal association between chlamydial infections and atherosclerosis. As the results obtained by different groups show considerable variations, we provide further data based on a highly specific and sensitive nested PCR method. Positivity was confirmed by nonradioactive hybridization with a specific probe, and sensitivity was determined by titration experiments. C. pneumoniae DNA was detected in 8/29 (28%) of carotid artery samples and 3/14 (21%) of aortic aneurysms.

Correlations between posterior gastric artery and superior polar artery in human anatomy.

We investigated the correlations in incidence and anatomy of 2 splenic artery branches, the Posterior Gastric Artery (PGA) and the Superior Polar Artery (SPA). In the literature these 2 branches were never described on one and the same splenic artery. We studied the splenic arteries of 126 corpses and found a cranio-sinistrally directed branch of the splenic artery in 76.2%. It appeared as a PGA (only stomachial supply) in 27.7% and as a SPA (only splenic supply) in 3.27%. In the most cases we detected an intermediate-type--we called it "gastrosplenic artery = GSA"--having a posterior gastric and a superior polar branch simultaneously. Such a "gastrosplenic artery" leaves the main trunk of the splenic artery in its middle segment in cranio--sinistral direction and falls apart into a posterior gastric and a superior splenic branch both with various differences in caliber. All these variations are described, nomenclature and the functional and surgical importance of these findings are discussed.

Computer simulation of the circulatory system during support with a rotary blood pump.

In order to investigate the performance characteristics of nonpulsatile centrifugal pumps and their interaction with the pulsating heart, a computer simulation model was developed. A model of the pump, including the cannulae and the interference of the cannula and the left atrial wall, was added to a simulator of the circulation. It was implemented on a PC-AT using the analog simulating software AGO1000. An interval of 1 msec real-time per calculation step was evaluated to provide stable results. The calculation speed was approximately 100 msec per step. First simulation studies showed that both the positioning and resistance of the cannulae exert a major influence on system performance and equalized the different pressure-flow characteristics of vaneless and impeller pumps (difference of dp/dQ decreases from more than 6 times without cannulae to 130% with cannulae). In addition, the effects of suction in the atrial cannula, and changes of ventricular performance during changes in pumping power, could be properly simulated. The comparison with animal tests proved that the model is a suitable tool for testing control algorithms for centrifugal pumps.

Prosthetic bypass and flow reversal in the dissecting thoraco-abdominal aortic aneurysm.

In 1981 Carpentier and Co-workers introduced an alternative surgical procedure for great dissecting thoraco-abdominal aortic aneurysms, departing from the resection and the orthotopic implantation of a prosthesis (graft inclusion technique). Compression of the aneurysmatic false lumen from the inside under stepwise thrombosis of the aneurysmal sac with conservation of the main arterial origins was achieved by prosthetic bypass of the diseased vascular part and a flow reversal in the dissected aortic region by an oblique suture across the aortic lumen after the origin of the left subclavian artery. This procedure, distinguished by rather little effort and few complications (bleeding, ischaemic spinal cord damage) is described for all stages of dissecting thoracal aortic aneurysms. In the last 2 years this operation was performed in our department on 4 patients (1 m. 3 f) suffering from an acute dissecting thoraco-abdominal aortic aneurysm (Stanford type B). 2 patients died in the early postoperative period, one from a redissection close to the proximal anastomosis, the other due to the critical cardiac situation. 2 patients could be followed up postoperatively 10 and 27 months. In both cases no signs of minor perfusion of the spinal cord, the kidneys, or the mesenterial organs were observed. In both cases a partial thrombosis of the aneurysmal sac with intact blood stream to the major vessels in these regions could be demonstrated by sonography, angiography or DSA, and computer tomography. The concept of flow reversal proved to be an alternative to major resection procedures.

Incidence, anatomy and territories supplied by the posterior gastric artery.

The posterior gastric artery, a branch of the splenic artery to the posterior gastric wall, was described for the first time by Walther in 1729. It was often recognized by many authors since, but consequently ignored by anatomical and surgical textbooks until its rediscovery and description by Suzuki et al. [Ann. Surg. 187: 134-136, 1978]. The incidence of the posterior gastric artery differs between 4 and nearly 100%. All authors describe posterior gastric regions being supplied by the posterior gastric artery, but sometimes also a branch running towards the superior pole of the spleen is cited. In our study of 104 corpses we found the posterior gastric artery with an incidence of 37.5%. In one third of these cases, a branch of the posterior gastric artery to the superior pole of the spleen was also detectable. Besides these results, the course of the posterior gastric artery to the corresponding organs and the importance of this vessel for the abdominal surgeon are discussed.

1,2-Dimethylhydrazine-induced carcinogenesis influenced by different colonic anastomoses in rats.

Dispensing subcutaneously 1,2-dimethylhydrazine, intestinal carcinogenesis was investigated in male Fisher rats with different surgical colonic anastomoses, producing blind gut loops of isoperistaltic high (fecal stasis) and anisoperistaltic low fecal contact. One hundred and eight rats, except 1 rat of the control group, developed colonic neoplasms. In contrast to the control group, mainly in anastomotic areas and in isoperistaltic blind gut loops with intensive fecal contact huge adenocarcinomas of exophytic growth appeared with a mean tumor diameter (MTD) of 1.9 +/- 0.7 to 2.2 +/- 0.8 cm. Even in the control group, where rats only underwent laparotomy, we observed small polypoid adenocarcinomas mainly located in the distal colon (MTD: 0.7 +/- 0.3 cm). Anastomotic areas and isoperistaltic blind loops with intensive fecal contact proved to be regions with a higher risk for carcinoma formation.

Experimental comparison of four methods of end-to-side anastomosis with expanded polytetrafluoroethylene.

BACKGROUND: Four established techniques of distal end-to-side anastomosis (direct anastomosis, Linton patch, Taylor patch and Miller cuff) were compared to investigate the local distribution of anastomotic intimal hyperplasia. The study aimed to elucidate whether mechanical factors or flow alterations are mainly responsible for the improved patency rates reported for vein cuff interposition techniques in infrainguinal arterial reconstructions using prosthetic graft material. METHODS: Thirty-two expanded polytetrafluoroethylene (ePTFE) femoropopliteal bypass grafts were implanted in 16 sheep using the four anastomotic techniques. After 6 months the grafts were explanted and examined histologically. The local distribution of intimal hyperplasia was determined, particularly for areas of material transition and of high and low shear stress. RESULTS: The mean amount and distribution of intimal hyperplasia were similar for all anastomotic types. Intimal hyperplasia was greatest along all transitions between ePTFE and venous patches, and between ePTFE and recipient artery. It was lower along the transitions between venous patches and artery, and was lowest at the host artery floor. CONCLUSION: Vein interposition did not reduce anastomotic intimal hyperplasia and did not change the distribution patterns of hyperplasia, which were influenced mainly by mechanical factors. The effect of vein interposition is to move areas of maximum intimal hyperplasia away from the small recipient artery up to the more capacious graft-patch anastomosis.

Intrarenal Doppler ultrasonography: which vessel should be investigated?

The aim of our study was to determine whether the site of intrarenal Doppler measurement influences diagnosis of renal artery stenosis. In an experimental test, three sheep with variable degrees of renal artery stenosis were investigated. In each animal, the resistive index from renal segmental arteries correlated better with mean pressure gradient (r = 0.85, 0.71, 0.85) and had lower standard deviation (s = 0.02 to 0.05) than resistive index from interlobar arteries (r = 0.48, 0.54, 0.61) (s = 0.03 to 0.11). In two animals the difference was significant (correlation: P < or = 0.01, P = 0.13, P < or = 0.05; standard deviation: P < or = 0.01, P < or = 0.34, P < or = 0.05). For detecting renal artery stenosis, vessels within the renal sinus should be used for Doppler sampling.

The contribution of extracranial blood oxygenation on near-infrared spectroscopy during carotid thrombendarterectomy.

To determine the contribution of extracranial oxygenation on regional cerebral oxygenation measured by an Invos 3100 near-infrared spectrometer, we measured oxygenation in blood drawn from both the facial vein (draining substantially blood from forehead areas) and the jugular venous bulb. There was no correlation between regional cerebral oxygenation and facial vein oxygenation (p = 0.35) but there was a significant correlation between regional cerebral oxygenation and jugular venous bulb oxygenation (p = 0.027). Linear regression analysis predicted a 3.6% change in regional oxygenation for every 10% change in jugular venous bulb oxygenation. We showed that extracranial tissue oxygenation had a negligible influence on the values recorded using near-infrared spectroscopy. Individual changes in jugular venous bulb oxygenation were poorly reflected. Data obtained by this near-infrared spectroscopy device are an unreliable guide to the adequacy of cerebral oxygenation.